Date registered: May 2016
Vehicle: 2000 S430, 2003 S430, 2003 S600 TT, and 2005 E320 CDI
Mentioned: 188 Post(s)
Quoted: 997 Post(s)
Spirtnoye, I'm a n00bie with these cars, only having started in 2016. Unlike Dave, I'm not a professional mechanic, more of a hobbyist, though I do take the hobby fairly seriously. Like you, I used to believe cars were so complex that only a "professional" could possibly understand them. This, as you also have discovered, is not necessarily the case.
Given your background, it sounds like you have a good idea how to tell if a car's been neglected or if it's been cared for. I'd look for one that's been cared for. Accept faults that you know that aren't too difficult to fix, e. g. suspension issues. Reject faults like body rust, which are difficult, or any faults with especially the 7-speed transmission.
I was actually surprised at how relatively easy the W220 is to work on. SDS is pretty much a must, as Dave said. I was one of the naysayers before that was looking for iCarsoft and Autel and the others, until I bought SDS and actually started using it. Yep, Dave's right. I often say that if I can do it, anyone can, and it really is true (I'm not all that smart!). My mechanic buddy has a couple of W220's and loves them. His daily driver is a 2003 S500.